1. Field of the Invention
The present invention relates to a sealing device for sealing a periphery of a rotary shaft in automobiles, general machines, industrial machines or the like, and the sealing device has a rotation detecting element of a rotary encoder.
2. Description of the Conventional Art
In the automobiles, rotation numbers and rotation speed of an axle, a crank angle of an engine (a rotation angle of a crank shaft) and the like are detected in order to measure travel speed and travel distance and to control ignition and fuel injection timing of an engine. Such the rotation detecting parts need to be sealed so that many trials were made for sealing. For example, it is known that a trial for saving a space for mounting a rotary recorder and a sealing device is made. This trial is indicated in Japanese Patent Application Laid Open No. 2002-48247. In this trial, a magnetized disc, which is a rotation detecting element of a magnetic type rotary encoder, is integrally provided to a sealing element on the rotation side of the sealing device for sealing the periphery of the rotary shaft.
That is, the sealing device indicated in Japanese Patent Application Laid Open No. 2002-48247 includes a seal lip fixed on the shaft hole housing side which is not rotated; and a slinger which is attached to the rotary shaft and contacted slidably and hermetically with the seal lip. The slinger is integrally adhered with the magnetized disc, which is made of a rubber-type elastic material mixed with magnetic powders and has magnetic poles alternate-differently in the circumferential direction. A magnetic sensor is provided on the stationary side so as to closely face the magnetized disc. Therefore, when the magnetized disc is rotated together with the slinger by rotation of the rotary shaft, a pulse signal is outputted from the magnetic sensor closely facing the magnetized disc in correspondence with the magnetic poles alternately passing near the detected face thereof.
However, as for the sealing device indicated in Japanese Patent Application Laid Open No. 2002-48247, a sealing and sliding section having the slinger attached with the magnetized disc and the seal lip slidably contacting with the slinger is to seal the dust on the atmosphere side as a sealing object. Thus, when engine oil is a sealing object, a structural element of the magnetic type rotary encoder is positioned in the engine oil atmosphere. Further, in this case, engine heat transmitted through the engine oil gives adverse effects to a magnetic field of the magnetized disc. Further, when sludge in the engine oil is attached on the surface of the magnetized disc by magnetic force, the sludge gives also adverse effects to the magnetic field of the magnetized disc. In such the cases, there is a problem that signal patterns outputted from the magnetic sensor may be disturbed.